An electronic device may include one or more circuit boards. A typical circuit board is a planar board that mechanically supports electronic components. The electronic components may comprise, for example, resistors, capacitors, switches, batteries, and other more complex integrated circuit components, i.e. microprocessors. The circuit board typically comprises a dielectric material, for example, a polymer material.
The circuit board may include conductive traces on the surface for connecting the electronic components to each other. As electronic circuitry has become more complex, multilayer circuit boards with at least two electrically conductive pattern layers have been developed. Typically, the different conductive trace layers of a multilayer circuit board may be connected through vertically extending vias, which comprise conductive materials, for example, metal.
A typical multilayer circuit board may comprise a plurality of core layers with bonding layers therebetween affixing the adjacent core layers together. Each core layer typically includes a dielectric layer with electrically conductive pattern layers on the opposing surfaces of the dielectric layer. Typically, during manufacture of the multilayer circuit boards, the core and bonding layers are stacked together and then heated and compressed (laminated) to cause the bonding layer to affix the adjacent core layers together.
One exemplary multilayer circuit board is a board that comprises an air-core dielectric waveguide structure. In other words, the multilayer circuit board includes a conductive core for transmitting the signal while adjacent portions of the multilayer circuit board provide an open area of air around the conductive core. As will be appreciated by those skilled in the art, the air-core serves as a dielectric material surrounding the conductive core and provides for reduced loss and reduced loading effects in the conductive core.
For example, U.S. Pat. No. 7,656,256 to Houck et al. discloses forming a multilayer circuit board to provide a coaxial air-core waveguide. The waveguide includes outer conductive layers forming a box-like outer conductor structure, and a pair of support arms extending inwardly from the outer conductive layers to support the inner conductor. The waveguide is formed during a multi-step process using a base substrate.
U.S. Pat. Nos. 7,405,638, 7,948,335, 7,148,772, and 7,012,489 to Sherrer et al. also disclose a coaxial air-core waveguide. The waveguide includes outer conductive layers forming a box-like structure, and a single lateral support arm extending inwardly from one of the outer conductive layers to support the inner conductor. In another embodiment, the support arm may extend from the bottom conductive layer to define a pedestal support arm. In one embodiment, the waveguides may be stacked to provide a plurality of coaxial waveguides.
U.S. Pat. No. 7,898,356 to Sherrer et al. also discloses a coaxial air-core waveguide. This coaxial air-core waveguide includes a single lateral support arm extending between opposing outer conductive layers.
In the typical approach to manufacturing air-core waveguide radio frequency (RF) structures, the process may include mature wafer lithographic build up on wafer substrates. When these devices are finished and are to be integrated onto a device wafer, the air-core waveguide RF structure may have to be diced and wire bonded to the appropriate next level assembly. Vibration from the dicing process may place the air-core waveguide RF structures at risk.
A second possible approach involves direct build-up of air core RF structures on the device wafer itself. Damascene-based formation of these air core conductive traces, and the associated chemical mechanical polishing (CMP) process may add risk to the integrity of the device wafer. Typical wafer substrates may not offer the most optimum RF properties for an RF substrate. Additionally, the thickness of the typical rigid wafer substrate may add undesirable size to the packaging of the air-core waveguide RF structure. For example, it impairs the use of the article in a restricted space.